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From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Dave Hansen <dave@linux.vnet.ibm.com>
Subject: Re: [Approach #2] [RFC][PATCH] Remove cgroup member from struct page
Date: Thu, 11 Sep 2008 08:38:20 +1000
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Cc: balbir@linux.vnet.ibm.com, kamezawa.hiroyu@jp.fujitsu.com,
       Andrew Morton <akpm@linux-foundation.org>, hugh@veritas.com,
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On Thursday 11 September 2008 08:21, Dave Hansen wrote:
> On Tue, 2008-09-09 at 18:20 -0700, Balbir Singh wrote:
> > +       start = pgdat->node_start_pfn;
> > +       end = pgdat->node_start_pfn + pgdat->node_spanned_pages;
> > +       size = (end - start) * sizeof(struct page_cgroup);
> > +       printk("Allocating %lu bytes for node %d\n", size, n);
> > +       pcg_map[n] = alloc_bootmem_node(pgdat, size);
> > +       /*
> > +        * We can do smoother recovery
> > +        */
> > +       BUG_ON(!pcg_map[n]);
> > +       return 0;
> >  }
>
> This will really suck for sparse memory machines.  Imagine a machine
> with 1GB of memory at 0x0 and another 1GB of memory at 1TB up in the
> address space.
>
> You also need to consider how it works with memory hotplug and how
> you're going to grow it at runtime.

I think it should try to hook into the physical memory model
code. I thought it was going to do that but didn't look at the
details...